> ## Documentation Index > Fetch the complete documentation index at: https://docs.labelbox.com/llms.txt > Use this file to discover all available pages before exploring further. # Hard stop a session immediately > Stops the session immediately and schedules durable sandbox teardown. The response confirms the session stopped; sandbox cleanup may continue asynchronously and is retried. An active Evaluation or one with unfinished clone cleanup returns retryable 409 evaluation_cancellation_pending before the session is stopped; retry after Evaluation cleanup finishes. A session that already reached a terminal status with no pending cleanup is left as it is, so the call is safe to repeat. ## OpenAPI ````yaml /managed-agents/openapi.yaml post /managed-agents/v1/sessions/{session_id}/cancel openapi: 3.1.0 info: title: Managed Agents API version: 0.14.0 description: >- The Recursion Managed Agents REST API. Authenticate with a Recursion API key as a bearer token. An organization-scoped key acts in its own organization and needs nothing else; a tenant-scoped key must also send `x-organization-id` with an organization id or `default`. Field names follow each operation's published schema. servers: - url: https://api.recursion.labelbox.com security: - bearerAuth: [] paths: /managed-agents/v1/sessions/{session_id}/cancel: post: tags: - Sessions summary: Hard stop a session immediately description: >- Stops the session immediately and schedules durable sandbox teardown. The response confirms the session stopped; sandbox cleanup may continue asynchronously and is retried. An active Evaluation or one with unfinished clone cleanup returns retryable 409 evaluation_cancellation_pending before the session is stopped; retry after Evaluation cleanup finishes. A session that already reached a terminal status with no pending cleanup is left as it is, so the call is safe to repeat. operationId: managedAgentsCancelSession parameters: - description: Session id (UUID) as returned by startSession or listSessions. in: path name: session_id required: true schema: description: Session id (UUID) as returned by startSession or listSessions. format: uuid type: string responses: '200': content: application/json: schema: $ref: '#/components/schemas/ManagedAgentsCancelledResponse' description: >- Response body of POST /v1/sessions/{session_id}/cancel. Cancel is terminal for the run but not for the record: the session is stopped and the sandbox torn down, while the session, its events, and its outcomes remain readable. The session row itself is removed from reads only by the separate soft-delete endpoint. '400': description: The request was rejected by schema or semantic validation. content: application/json: schema: $ref: '#/components/schemas/ManagedAgentsApiErrorInvalidRequest' '401': description: The caller is unauthenticated. content: application/json: schema: $ref: '#/components/schemas/ManagedAgentsApiErrorUnauthorized' '403': description: The caller lacks a required permission or capability. content: application/json: schema: $ref: '#/components/schemas/ManagedAgentsApiErrorForbidden' '404': description: No such resource is reachable for this caller. content: application/json: schema: $ref: '#/components/schemas/ManagedAgentsApiErrorNotFound' '409': description: >- The request conflicts with the resource state, or with an in-flight idempotent replay. content: application/json: schema: $ref: >- #/components/schemas/ManagedAgentsApiErrorEvaluationCancellationPending '429': headers: Retry-After: description: When to retry, as delay seconds or an HTTP date. schema: type: string description: A rate limit is exhausted. Honor `Retry-After`. content: application/json: schema: $ref: '#/components/schemas/ManagedAgentsApiErrorRateLimitExceeded' '500': description: An unexpected server-side failure. content: application/json: schema: oneOf: - $ref: '#/components/schemas/ManagedAgentsApiErrorInternalError' - $ref: >- #/components/schemas/ManagedAgentsApiErrorInvariantViolation discriminator: propertyName: code mapping: internal_error: $ref: '#/components/schemas/ManagedAgentsApiErrorInternalError' invariant_violation: $ref: >- #/components/schemas/ManagedAgentsApiErrorInvariantViolation '502': description: The service returned an invalid response. content: application/json: schema: $ref: '#/components/schemas/ManagedAgentsApiErrorBadGateway' '503': description: >- A dependency is unavailable. Consult details.retryable and Retry-After when present before retrying. content: application/json: schema: oneOf: - $ref: >- #/components/schemas/ManagedAgentsApiErrorManagedAgentsUnavailable - $ref: >- #/components/schemas/ManagedAgentsApiErrorServiceUnavailable discriminator: propertyName: code mapping: managed_agents_unavailable: $ref: >- #/components/schemas/ManagedAgentsApiErrorManagedAgentsUnavailable service_unavailable: $ref: >- #/components/schemas/ManagedAgentsApiErrorServiceUnavailable '504': description: The service did not respond before the timeout. content: application/json: schema: $ref: '#/components/schemas/ManagedAgentsApiErrorGatewayTimeout' components: schemas: ManagedAgentsCancelledResponse: description: >- Response body of POST /v1/sessions/{session_id}/cancel. Cancel is terminal for the run but not for the record: the session is stopped and the sandbox torn down, while the session, its events, and its outcomes remain readable. The session row itself is removed from reads only by the separate soft-delete endpoint. properties: cancelled: description: >- Always true. The session was stopped and the sandbox closed; failures are HTTP errors instead, so this field never reports false. It is also true when the session had already reached a terminal state, making cancel safe to retry. type: boolean required: - cancelled type: object example: cancelled: true ManagedAgentsApiErrorInvalidRequest: type: object properties: code: type: string minLength: 1 description: Stable machine-readable error code. enum: - invalid_request message: type: string minLength: 1 description: Human-readable error message. details: $ref: '#/components/schemas/ManagedAgentsApiErrorDetails' description: >- Optional structured error details. Reserved transport fields are typed; code-specific fields remain forward compatible. required: - code - message additionalProperties: false description: Standard flat error response. ManagedAgentsApiErrorUnauthorized: type: object properties: code: type: string minLength: 1 description: Stable machine-readable error code. enum: - unauthorized message: type: string minLength: 1 description: Human-readable error message. details: $ref: '#/components/schemas/ManagedAgentsApiErrorDetails' description: >- Optional structured error details. Reserved transport fields are typed; code-specific fields remain forward compatible. required: - code - message additionalProperties: false description: Standard flat error response. ManagedAgentsApiErrorForbidden: type: object properties: code: type: string minLength: 1 description: Stable machine-readable error code. enum: - forbidden message: type: string minLength: 1 description: Human-readable error message. details: $ref: '#/components/schemas/ManagedAgentsApiErrorDetails' description: >- Optional structured error details. Reserved transport fields are typed; code-specific fields remain forward compatible. required: - code - message additionalProperties: false description: Standard flat error response. ManagedAgentsApiErrorNotFound: type: object properties: code: type: string minLength: 1 description: Stable machine-readable error code. enum: - not_found message: type: string minLength: 1 description: Human-readable error message. details: $ref: '#/components/schemas/ManagedAgentsApiErrorDetails' description: >- Optional structured error details. Reserved transport fields are typed; code-specific fields remain forward compatible. required: - code - message additionalProperties: false description: Standard flat error response. ManagedAgentsApiErrorEvaluationCancellationPending: type: object properties: code: type: string minLength: 1 description: Stable machine-readable error code. enum: - evaluation_cancellation_pending message: type: string minLength: 1 description: Human-readable error message. details: $ref: '#/components/schemas/ManagedAgentsApiErrorDetails' description: >- Optional structured error details. Reserved transport fields are typed; code-specific fields remain forward compatible. required: - code - message additionalProperties: false description: Standard flat error response. ManagedAgentsApiErrorRateLimitExceeded: type: object properties: code: type: string minLength: 1 description: Stable machine-readable error code. enum: - rate_limit_exceeded message: type: string minLength: 1 description: Human-readable error message. details: $ref: '#/components/schemas/ManagedAgentsApiErrorDetails' description: >- Optional structured error details. Reserved transport fields are typed; code-specific fields remain forward compatible. required: - code - message additionalProperties: false description: Standard flat error response. ManagedAgentsApiErrorInternalError: type: object properties: code: type: string minLength: 1 description: Stable machine-readable error code. enum: - internal_error message: type: string minLength: 1 description: Human-readable error message. details: $ref: '#/components/schemas/ManagedAgentsApiErrorDetails' description: >- Optional structured error details. Reserved transport fields are typed; code-specific fields remain forward compatible. required: - code - message additionalProperties: false description: Standard flat error response. ManagedAgentsApiErrorInvariantViolation: type: object properties: code: type: string minLength: 1 description: Stable machine-readable error code. enum: - invariant_violation message: type: string minLength: 1 description: Human-readable error message. details: $ref: '#/components/schemas/ManagedAgentsApiErrorDetails' description: >- Optional structured error details. Reserved transport fields are typed; code-specific fields remain forward compatible. required: - code - message additionalProperties: false description: Standard flat error response. ManagedAgentsApiErrorBadGateway: type: object properties: code: type: string minLength: 1 description: Stable machine-readable error code. enum: - bad_gateway message: type: string minLength: 1 description: Human-readable error message. details: $ref: '#/components/schemas/ManagedAgentsApiErrorDetails' description: >- Optional structured error details. Reserved transport fields are typed; code-specific fields remain forward compatible. required: - code - message additionalProperties: false description: Standard flat error response. ManagedAgentsApiErrorManagedAgentsUnavailable: type: object properties: code: type: string minLength: 1 description: Stable machine-readable error code. enum: - managed_agents_unavailable message: type: string minLength: 1 description: Human-readable error message. details: $ref: '#/components/schemas/ManagedAgentsApiErrorDetails' description: >- Optional structured error details. Reserved transport fields are typed; code-specific fields remain forward compatible. required: - code - message additionalProperties: false description: Standard flat error response. ManagedAgentsApiErrorServiceUnavailable: type: object properties: code: type: string minLength: 1 description: Stable machine-readable error code. enum: - service_unavailable message: type: string minLength: 1 description: Human-readable error message. details: $ref: '#/components/schemas/ManagedAgentsApiErrorDetails' description: >- Optional structured error details. Reserved transport fields are typed; code-specific fields remain forward compatible. required: - code - message additionalProperties: false description: Standard flat error response. ManagedAgentsApiErrorGatewayTimeout: type: object properties: code: type: string minLength: 1 description: Stable machine-readable error code. enum: - gateway_timeout message: type: string minLength: 1 description: Human-readable error message. details: $ref: '#/components/schemas/ManagedAgentsApiErrorDetails' description: >- Optional structured error details. Reserved transport fields are typed; code-specific fields remain forward compatible. required: - code - message additionalProperties: false description: Standard flat error response. ManagedAgentsApiErrorDetails: type: object properties: field: description: >- Request field or header responsible for the error, when one can be identified. type: string issues: description: >- Boundary-validation failures as path-prefixed human-readable messages. type: array items: type: string requestId: description: Request correlation identifier for support and log lookup. type: string retryable: description: >- Server advice about failure transience. `true` means transient, `false` means non-transient, and absence gives no advice. Automatic replay is allowed only when this field is not `false` and the operation-specific retry and idempotency contract permits replay. type: boolean additionalProperties: {} description: >- Optional structured error details. Reserved transport fields are typed; code-specific fields remain forward compatible. securitySchemes: bearerAuth: type: http scheme: bearer description: A Recursion API key, created in the console under API keys. ````